Giant molecular clouds: what are they made from, and how do they get there?
Giant molecular clouds: what are they made from, and how do they get there?
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巨大的分子云：它们是由什么构成的，它们是如何到达那里的？
DOI：
10.1111/j.1365-2966.2012.21558.x
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发表时间：
2012
影响因子：
4.8
通讯作者：
Andreas Burkert
中科院分区：
文献类型：
--
作者：
C. Dobbs;J. Pringle;Andreas Burkert
我们分析了孤立星系的四个模拟的结果：两个与固定模式速度的刚性螺旋势，但与不同程度的星星形成诱导反馈，一个与轴对称星系的潜力和一个“活”的自引力恒星组件。由于我们使用拉格朗日方法，我们能够选择在特定时间范围内位于巨分子云（GMC）内的气体，然后研究这种气体在早期和晚期的性质。我们发现，气体形成GMCs是不典型的星际介质（ISM）至少50万年前的云形成，并达到平均密度的数量级内的平均云密度约10万年前的云形成。GMC中的气体在被恒星反馈扩散后至少需要5000万年才能恢复到典型的ISM气体，并且在某些情况下，气体永远不会完全回收。我们还提出了一个研究的2D，垂直平均速度场内的ISM。我们表明，速度场对应于最短的时间尺度（即那些时间尺度最接近的云的立即形成和消散）可以很容易地理解的各种云的形成和消散机制。流动模式的特性可以用来区分驱动会聚流（例如螺旋冲击，超新星）的过程，从而分子云的形成，我们注意到，这种特性可能是检测与附近星系的未来观测。
We analyse the results of four simulations of isolated galaxies: two with a rigid spiral potential of fixed pattern speed, but with different degrees of star formation induced feedback, one with an axisymmetric galactic potential and one with a ‘live’ self-gravitating stellar component. Since we use a Lagrangian method, we are able to select gas that lies within giant molecular clouds (GMCs) at a particular time frame, and then study the properties of this gas at earlier and later times. We find that gas which forms GMCs is not typical of the interstellar medium (ISM) at least 50 Myr before the clouds form and reaches mean densities within an order of magnitude of mean cloud densities by around 10 Myr before cloud formation. The gas in GMCs takes at least 50 Myr to return to typical ISM gas after dispersal by stellar feedback, and in some cases the gas is never fully recycled. We also present a study of the 2D, vertically averaged velocity fields within the ISM. We show that the velocity fields corresponding to the shortest time-scales (i.e. those time-scales closest to the immediate formation and dissipation of the clouds) can be readily understood in terms of the various cloud formation and dissipation mechanisms. Properties of the flow patterns can be used to distinguish the processes which drive converging flows (e.g. spiral shocks, supernovae) and thus molecular cloud formation, and we note that such properties may be detectable with future observations of nearby galaxies.